I'm sure I don't understand how it works, and not just because it makes me want to sit on the sofa with a glass and smoke

Well, what I wanted was a frequency shifter where I can morph the controlling sine/cosine osc into other waveforms. Basically a frequency shifter is like a ringmodulator but with separate lower and upper sidebands available. (Jan, I know you know this but maybe others don't.) It works by using two ringmodulators and waveforms where all the partials have a phase difference of 90 degrees. Regrettably the G2 does not have a separate osc module that provides these two waves and the frequency shifter module does only work with an internal sine/cosine oscillator where the waveform cannot be morphed into something with more harmonics. So, I had to patch such an osc myself.

In fact, this oscillator is a digital emulation of an analog sine<->saw osc that I once designed and have used in those 'blippoboxes'. This osc is a biquad-type oscillator, meaning that it has two stages (the 'bi' in biquad) that produce a phaseshift of 90 degrees (which is the 'quad' of 360 degrees) plus an inverter (the remaining two quads) in the oscillation feedback loop, which has a gain of a little over unity to make the loop oscillate and a slight HF damping to not make it also oscillate at half the sample rate. In the feedback loop is also a limiter to keep the oscillation stable. An analog version always starts to oscillate due to the little noise always present in such a circuit, but the digital version has to start by feeding it just a little bit of noise. The digital emulation regrettably stops oscillating at a couple of kiloHertz, which is caused by some bandwidth issues I will not go into this time. In contrast, my analog design can produce a stable waveform from half a Hertz up to 50 kHz when quality components are used.

This oscillator produces both a sinewave and a cosine wave at the outputs of the two 'quad' stages (allpass filters are used to really get 90 degrees phase shift in each stage). By additionally using LinFM selfmodulation the waveform can be morphed between a reasonably pure sine and a waveform containing a series of all harmonics, like those in a sawtooth waveform. But as the harmonic series is build up from the fundamental it gives quite a warm sound, like a softly filtered traditional sawwave. The selfmodulation has to be linear and it has to pass though a highpass filter to avoid unwanted detuning and keeping the modulation index reasonably constant over the frequency range. The interesting thing is that when this selfmodulation is applied all partials in the two outputs still have that 90 degree phase difference relation and so such a waveform can be used to drive a frequency shifter. This gives the frequency shifter a more 'vintage ringmodulator' sound and makes it nice to process percussive sounds and spacey drones.

There are four of these biquad oscillators in the patch. The allpass filters are made with a crossfader and a mixer subtracting twice the output of the crossfader (basically a 6dB lowpass filter) from the input. The crossfader is used as this one can be modulated linearly and the standard -6dB lowpass filter modules cannot.

Two multimode 'state variable' filters are used to create a 'twin peaks' percussive element. The nice thing about these filters is that the phase difference between the BP and LP output at resonance is also 90 degrees, and can so be used in the frequency shifter circuit without having to patch a Hilbert-transform phase shifting network.

Doing it this way there are many extra control points, knobs and modulations possible compared to the standard frequency shifter module. Knobs and modulations that all seem to enhance that fifties type of 'Forbidden planet' sounds that I personally like quite a lot.

When I had this working it was just too tempting to add some distortion, some echo and some other little ditties, and then I had to go to do real work for money. But before I went out I thought it nice to publish the patch, just as it is quite experimental. And I probably should post much more experimental patches.

Jan, now that you had your smoke and drink, followed by these hints, I guess it is not so difficult to figure out, it is actually quite structured. So, I do expect a 'verkrachte versie' some time soon.

Incredible! this is an inspiring Patch
only dont have enough expanded memory to run it all , but the most important is the 2nd patch for me
and by the way i was your student in 2006, and i am very greatfull many thx
Jose

Edit : hmm .. the patch archive - or the attachment archive is corrupted it seems - nothing demo friendly on that patch .. prolly it got lost in the 2007 crash and the file id was taken later by some other patch .. which opens as a performance even when named as a pch ... weird ... and just now I finally got off that sofa

Edit2: tried to fix it, but the patch is really gone .. sorry._________________Jan

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